Many manufacturing machines, such as printing presses, cigarette-making machines and bag-making machines, utilize a continuous ribbon or band or web of raw material to manufacture a stream of finished product. Such machines utilize a variety of materials, including paper, cardboard and thin metal foil. Often this web material is provided to the manufacturing machine from a large, continuous roll of material which may comprise several thousand feet of web material. In operation, the utilization machinery draws the web material from the supply roll at a high rate of speed which may approach several hundred feet per minute.
Often, the web material follows a tortuous path through such machines and a considerable amount of time must be spent in initially setting up the machine prior to operation to ensure the web material is under proper tensions and follows the correct path through the machine. Consequently, it is advantageous to provide a continuous supply of web material to the machine to avoid having to stop the machine at the end of each roll of web material and rethread the mechanism as each roll of web material becomes exhausted.
Accordingly, various splicing mechanisms have been devised to splice the leading edge of a new roll of web material (called the "ready roll") to the trailing edge of an expiring roll of material (called the "running roll") while the utilization machine is operating to provide a continuous strip of web material to the utilization machine.
Several different types of splicing machines have been developed to automatically perform such a splicing operation. In these machines, a splice is usually made by adhering the leading edge of the ready roll to a portion of the running roll of web material by means of cement or double-faced, pressure-sensitive tape and then severing the web from the running roll behind the splice.
In order to form a reliable splice, the web material in the ready and running rolls must be moving at approximately the same speed. Conventional splicing machines accomplish speed matching in two different ways. "On-the-fly" splicers utilize an electric motor or other driving means to accelerate the ready roll so that its web material is travelling at the same speed as the web material is being drawn from the running roll. The splicing operation is actually performed "on-the-fly" as the two webs are moving through the splicing apparatus.
In "zero-speed" splicers, the running roll of web material is braked nearly to a stop and the splicing operation is performed while the webs from both the ready roll and the running roll are substantially stopped. Since, as previously mentioned, it is usually not desirable to stop the utilization machine during the splicing operation, a web "accumulator" or "festooner" is provided between the utilization machine and the splicing apparatus. The accumulator consists of a bank of fixed rollers and a bank of opposing, movable rollers and the web material is wound between the rollers in a festoon fashion to provide a large slack loop. During the splicing operation when the web material has been substantially stopped, the roller banks move together to provide the necessary web material to keep the manufacturing machine in operation. After the splice is completed, the ready roll of material is accelerated to its running speed and a feedback mechanism controls the web accumulator to return the movable rollers to their normal position.
In a typical zero-speed splicer, the two webs are pressed together to form a splice by a pair of resilient "nip rollers". Prior to a splicing operation, the leading edge of the ready roll must be prepared for splicing and placed on one of the nip rollers. The nip rollers are provided with a row of holes and are connected to a vacuum source applied to the nip roller and thus the web material adheres to the roller and is held in position until the splice is made.
Preparation of the leading edge of the ready roll involves trimming the web edge squarely and applying cement of a strip of gummed tape to adhere the edge to the other web. Typically, on prior art machines such preparation is done on such a "vacuum bar" mounted in front of the nip rollers. The first step in splice preparation is to release a braking mechanism on the ready roll and draw the web material over the vacuum bar. At this point vacuum is applied to the vacuum bar holding the web material in place. A knife or razor is then used to trim leading edge of the web material squarely and then cement or splicing tape is applied to the edge. The vacuum is then removed, the prepared edge is transferred from the vacuum bar to the one of the nip rollers and vacuum then is reapplied, causing the web material to adhere to the nip roller. Finally, the nip roller and the prepared edge is rotated into splicing position, usually directly opposite the other nip roller.
At this point, the operator preparing the splicing machine must manually rotate the ready roll of web material and reapply the brake, thereby removing any slack in the web to prevent breakage of the web when the splicing operation is subsequently performed.
The splicing machine is then ready to automatically splice the ready roll to the running roll. In order to do this, the splicing machine monitors the diameter of the running roll and, when a predetermined diameter is reached the splicing mechanism brakes the expiring roll of material to a stop, automatically brings the nip rollers together causing the leading edge of the ready roll to adhere to a portion of the running roll, and operates an automatic knife to sever the running roll behind the splice. Depending on the proximity of the knife to the nip rollers, a trailing flap of material known as a "trailer" is left at the splice location. However, in most utilization machines, the trailer does not cause a significant problem. At the end of the splicing operation, the nip rollers automatically separate and an acceleration motor accelerates the ready roll to running speed.
One of the problems with the prior method of preparing the leading edge of the ready roll for splicing is that it is difficult to properly trim the leading edge of the web material in order to produce a square cut. If the edge of the web material is not severed at a precise right angle to the material, the resulting splice is not straight causing uneven tension and allowing the web material to run off its guiding rollers, in turn, causing a breakage of the web material and the consequent interruption of the of the manufacturing process.
In addition, with prior art devices, since the web material must be removed from the vacuum bar and transferred to the nip rollers, it was often possible to apply the web material to the nip roller in a slanted position even though the edge was cut squarely also resulting in web breakage.
In order to overcome these problems some prior art splicing machines allow preparation of the leading edge of the ready roll while it is mounted on the nip rollers. In these machines, during web preparation, the web is drawn over the nip roller and placed on the vacuum bar which is located in front of the nip rollers. System vacuum is then turned on causing the web to adhere to the vacuum bar. The web material can then be trimmed with a razor using the edge of the vacuum bar as a guide. However, since the vacuum bar is located in front of the nip rollers it is possible to cut into the resilient nip rollers in the process of trimming the web, thereby damaging the splicing machine.
In addition, most prior art splicing machines expose the operator to the web severing knife which is operated by the automatic splicing machine during a splicing operation. As this knife is extremely sharp these machines present a safety hazard.
Futher, in most prior art machines, adjustment of the prepared web of material to remove slack often required considerable skill in operating the vacuum and brake controls in order to provide correct tension on the web material. It was also possible during a tensioning operation to pull the web off the nip roller thereby requiring the operator to redo the whole splice preparation resulting in wasted time and effort.
It is therefore an object of the present invention to allow preparation of the leading edge of the ready roll directly on the nip rollers.
It is another object of the present invention to provide as web splice preparation mechanism which automatically introduces the correct amount of slack and tension in the web material during splice preparation.
It is a further object of the present invention to provide a web splice preparation mechanism which is simple to operate and easy to maintain.
It is yet a further object of the present invention to provide a splice preparation mechanism which does not expose the operator's hand or fingers to the web severing knife.
Still a further object of the present invention is to provide a web splice preparation mechainsm which automatically positions a trimming blade in front of the nip rollers so that the edge of the web material may be torn off while the material is adhering to a nip roller.